Liquation of antimony sulfide



I 2,890,102 LIQUATION or ANTIMONY SULFIDE Unite Sta e BaIrfl 'O Willard S. Bundy, North Massapequa, N. assignor to No Drawing. Application June 3,1955 Serial No. 513,159

9-Claims. (Cl. 231 36) This invention relatesto the liquation of antimony sulfide and to the preparation of antimony sulfide in larger crystals that are of increased purity'with relation to the starting material- Pure antimony sulfide contains 28.3% sulfur as sulfide. Commercially available antimony sulfide of the stibnite variety usually contains less than the theoretical sulfidesulfur and sometimes contains even less than thereof. Such antimony sulfide when melted and cast produces an ingot containing short, fine needle shaped crystals in parallel arrangement. On crushing and grinding, this material gives rise to excessive amounts of dust. Furthermore, the crucible used for melting this material becomes coated with a heavy difiicult fusible scab which seriously interferes with the heat transfer through the crucible to the material as required in its processing.

It is the general object of this invention to provide a novel and improved process of liquation of antimony sulfide with an agent possessing acidic properties in the molten state to provide an improved purity, larger crystal antimony sulfide.

Another object is to remove iron compounds and antimony oxide from antimony sulfide when processed.

Another object of the invention is to promote more rapid melting of antimony sulfide by improved heat transfer.

A further object of the invention is to minimize oxidation of the charge during liquation incident to purification of antimony sulfide.

The foregoing and other objects of the invention are achieved by practice of the invention as set forth in detail hereinafter.

Example I In one example'of the invention, 10% by weight of Calgon" a detergent was used, and which is represented to be essentially sodium meta-phosphate. About 10% Calgon (used as a fiuxing material) about 3% by weight of sulfur and about 87% by Weight of crude antimony sulfide containing 26.2% total sulfur were placed in a crucible and heated in a furnace. The material was stirred occasionally to test for fluidity. After the contents of the crucible have been heated to a barely perceptible red glow such as 600 to 700 degrees centigrade, they are completely liquid, which color and fluidity are indications that the operation is complete. After processing, the antimony sulfide is cast in suitable molds, such as cast iron pots or molds and allowed to cool. The flux and occluded impurities form an upper layer over the antimony sulfide and are readily removed therefrom by chipping them off.

The flux material floats on the surface of the molten antimony sulfide and protects it against oxidation. The meta-phosphate flux also extracts iron compunds, particularly oxides, from the antimony sulfideand carries them into the top phosphate layer on the crucible.

The crucible used may be made from any material not reactive with antimony, antimony sulfide or the fluxing 2,890,102 .l atented June 9, 1959 compounds. Crucibles made from silicon carbide'plus carbon, for example, may be used with phosphate fluxes.

The used meta-phosphate flux can ordinarily hereused one 'or more times in the process and the metapho'sphate flux solidifies in the form of a glass-like material, generally brick red in color. As long as the flux material is transparent or translucent, it may be reused in the process, but when the material is mottled, or opaque it should be discarded from further use in the method of the invention.

The antimonysulfide produced generally crystallizes in larger needle crystals of greater cross section than prior crystals and they originate from several single points star.fashion. The product appears cleaner and more silverish than the starting materia v The crucibles used havebeen cleaner over longer periods of service and heat flow to the antimony sulfide in facilitated by the process of the'invention, in comparison with prior art practices. For example, in comparable eight hour shifts,.700 pounds of antimony sul-' fide was processed by prior art techniques while 1000 pounds of the sulfide was processed by practice of this invention.

Alkali meta-phosphates, or mixtures thereof that melt below about 825 degrees centigrade can be used in the process. Thus potassium meta-phosphate may be used in place of the sodium meta-phosphate, or materials that break down into a desired phosphate on heating, such as sodium ammonium acid phosphate (micro cosmic salt), or sodium dihydrogen phosphate, or its hydrate may be used in quantities to provide at least about 3% phosphate for each batch of the antimony sulfide being processed. Borax, boric oxide, boric acid also may be used in place of the phosphates in similar quantities.

The free sulfur is used in the reaction to make up any deficiency of sulfide sulfur and as an insurer to minimize loss of antimony sulfide in the processing and is not essential to the purification action of the fiuxing agent, or to the improved heat transfer action of such material as set forth hereinbefore. Preferably about 40 to 50% excess sulfur over that required to make up the deficiency of sulfide sulfur in the original charge is used as that aids in upgrading the starting antimony sulfide.

In view of the foregoing, it is considered that the objects of the invention have been secured.

While one complete embodiment of the invention has been disclosed herein, it will be appreciated that modification of this particular embodiment of the invention may be resorted to without departing from the scope of the invention as defined in the appended claims.

What is claimed is:

1. A method of processing antimony sulfide to improve the purity thereof comprising melting by heating a mixture of about 3% of an alkali meta-phosphate, and about 97% by weight of crude antimony sulfide, and casting the melt to provide an ingot with improved purity, larger crystal antimony sulfide therein and with a phosphate slag layer thereon.

2. A method of processing antimony sulfide to improve the purity and crystal structure thereof comprising melting by heating a mixture of about 3% sodium metaphosphate, and about 97% by weight of crude antimony sulfide in an inert crucible and casting the melt to provide an ingot with improved purity antimony sulfide therein and with a slag layer of phosphates thereon.

3. A method of processing antimony sulfide to improve the purity thereof comprising melting by heating a mixture of about 3% sodium meta-phosphate, about 3% sulfur, and about 94% by weight of crude antimony sulfide in an inert crucible, cooling and casting the melt to provide an ingot with improved purity larger crystal antimony sulfide therein than the starting material, and

with a phosphate slag layer thereon, and removing the slag layer from the remainder of the ingot.

4. A method of processing antimony sulfide to improve the purity thereof comprising melting by heating to about 600 to 700 -C.ia. mixtureof about.3% sodium meta-phosphate, sulfur,. and crude antimony sulfide in an 'inert crucible, cooling and casting the melt toiprovide an ingot with improved purity, larger crystal antimony sulfide therein than the starting material, and with a phosphate slag layer thereon, and removing the slag layer from the remainder of the ingot.

5. The method of purifying relatively impure antimony sulfide which comprises heating a mixture of at least 3% by weight of an alkali meta-phosphate and about 97% by weight of'the impure antimony sulfide tomelt it, jpermitting themixture to cool,and separating 'thepurified antimony sulfide from the cooledmixture.

6. A method of processing antimony sulfide toimprove the purity and crystal structure thereof comprising heating a rnixture' of at least'about 3% boric oxide, and the remainder .of crude antimony sulfide in an inert crucible to about 700 degress centigrade until all of the materials are melted, and casting the melt to provide an ingot with improved purity antimony sulfide therein and With a slag layer ofborates thereon.

7. A method of processing antimony sulfide to improve the purity and crystal structure thereof comprising heating amixtur e of at least about 3% borax, and the re- -mainder --of crude antimony sulfide in an inert crucible to about 700 degrees centigrade until all of the materials are melted, and casting the melt to provide an ingot with improved purity antimony sulfide therein and with a slag layer of borates thereon.

8. A method of processing antimony sulfide to improve the purity thereof comprising heating to melting a mixture of a material from the group consisting of an alkali meta-phosphate, boric oxide, and borax in about 3% by weight, and about 97% by weight of-crude antimony sulfide, and casting the melt to provide'a'n ingot with improved purityrlargercrystal antimony: sulfide therein and with a slag layer containing the flux and impurities thereon.

9. A method of "processing antimony sulfide to improve the purity thereof comprising heating to about 600 to 700 C. a mixture of a material from the group consisting of an alkali meta-phosphate, boric oxide, and borax in about 3% by weight, about 3% sulfur, andabout 94% by weight of crude antimony sulfide, andcasting the melt to provide an ingot with improved purity-larger crystal antimony sulfide therein and with a slag layer containing the-flux and impurities thereon.

No references cited. 

1.
 8. A METHOD OF PROCESSSING ANATIMONY SULFIDE TO IMPROVE THE PURITY THEREOF COMPRISING HEATING TO MELTING A MIXTURE OF A MATERIAL FROM THE GROUP CONSISTING OF AN ALKALI META-PHOSPHATE, BORIC OXIDE , AND BORAX IN ABOUT 3% BY WEIGHT, AND ABOUT 97% BY WEIGHT OF CRUDE ANTIMONY SULFIDE, AND CASTING THE MELT TO PROVIDE AN INGOT EITH IMPROVED PURITY LARGER CRYSTAL ANTIOMONY SULFIDE THEREIN AND WITH A SLAG LAYER CONTAINING THE FLUX AND IMPURITIES THEREON. 